Technology Services

Scanning Practices

Successful imaging in Powerpoint often proves to be a frustrating task: pictures that look clear on your screen lack clarity when projected; presentations with many images create a final file-size that is enormous and unwieldy.

This document will familiarize you with the basics of scanning and image preparation, and get your PowerPoint images to display clearly and consistently.

A Rule of Thumb

If nothing else, remember the following:

• Do not resize images at all in PowerPoint.
• PowerPoint is not an image editor, and resizing images within the PowerPoint environment is the #1 cause of image deterioration.
• Because PowerPoint will resize an image upon import if its size exceeds the dimensions of the PowerPoint stage, a good rule of thumb is to always verify that your image has not been resized. To do this, right-click on the image and choose Format Picture, then choose the Size tab. If either the Height and/or Width fields do not read 100%, change them to this value (be sure Lock Aspect Ratio is selected). If it is either too big or too small at 100%, it needs to be re-formatted in an image-editing program like Photoshop.

Initial Considerations

There are two important variables that you should consider before scanning or importing an image:

1. Resolution—What is the resolution of the computer I will be presenting on?
   
   

   For Larner College of Medicine faculty who will likely use the LCD projectors in LCOM classrooms, this means a resolution of 800 x 600, or whatever the computer’s resolution is set to. It is a good practice to make a note of a presentation’s target resolution, and check that the display device is set to that same resolution whenever it is presented. On most computers this can be accessed in Start > Settings > Control Panel > Display > Settings > Screen Area.

2. Size—How much of the PowerPoint screen is the image going to display?

If your image has more pixels than the resolution supports, it will contain extra data that serves no real purpose, and will bloat the presentation’s file-size unnecessarily. Even if you manually resize the image in Powerpoint (which is discouraged, as explained later), the image size stays the same.

So, assuming we’ve defined 800 x 600 as our target display resolution, and an image that took up about half of the PowerPoint screen, we would be shooting for an image that was about 400 pixels (width) by 300 pixels (height). Having a general idea of how big your image will be in relation to the total slide will help decide the settings you use to scan your image. After you’ve arrived at a general target image size, you are ready to begin scanning.

Acquiring the Image

Place the Document on the Scanner

Place the image or slide to be scanned face down on the scanner. Close the lid.

Open Scanning Software

Open your scanning software or image-editing program and begin acquiring a new scan. In Photoshop, this is often found under File > Import.

Preview Scan

Chose Preview to preview the scan.

Select A DPI

If you are scanning a slide:

Use the crop tool to select only the area to be scanned, e.g. the film without the border (if you are using a flatbed scanner). Based on the desired size you’ve established (in inches, based on Powerpoint stage size of 10” x 7.5”), select a DPI based on the table below, and remember it’s a good practice to start at about 2x the size, so you have more picture information to work with. We will resize it later.

If you are not scanning a slide:

In most cases the media you are scanning will not take up the entire scanner area. The scanner software should have a crop tool which allows you to zero in on the area you would like to scan. Use this tool to tell the scanner which area to scan, and be sure to leave a margin for some breathing room later.

While slides come in a universal size and make choosing the right settings relatively easy, all other documents (photos, news clippings, etc.) are non-standardized when it comes to size, and choosing the right settings requires a bit of trial and error. In most cases, 300 DPI is a good resolution, but try experimenting with different DPI settings.

Scan the Image

Hit Scan to scan the image.

Save the Uncompressed Image Before Editing

Save the image as a PSD or TIF, with a filename of ‘filename_raw, filename_orig’ or something similar to denote this is the raw, unedited version of the image. Because JPG’s are compressed and suffer a loss in quality each time they are saved, it is always wise to save the file in an uncompressed format: PSD in Photoshop, or TIF in any other program (vs. JPG, GIF and PNG, which compress the image). This allows us to revert to the original uncompressed version of the image without having to go through the trouble of re-scanning.

Save a Working Copy

Save the image as a PSD or TIF, with a filename of ‘filename’ or anything similar as long as it is different than the ‘raw’ version you saved initially. If you do not do this step, you run the risk of mistakenly overwriting the uncompressed version of the image which we want to preserve for any future edits we may want to make.

Edit Image

Using the image editing tools, rotate and crop the image as desired and make any changes to levels, contrast, etc. If you are using Photoshop, try Image>Adjust>Auto Levels and Image>Adjust>Auto Contrast. If you are not happy with the results, try adjusting these parameters manually with Image>Adjust>Levels and Image>Adjust>Brightness/Contrast.

Convert DPI and Resize

When you are happy with the image, change the DPI to 96 and change the width (or height) to the desired size. In Photoshop, choose Image > Image Size (be sure the Constrain Proportions option is selected).

Why 96 DPI? While most computer screens project at 72 DPI, some of the newer monitors use a higher DPI of 96. Choosing 96 DPI will add some ‘versatility’ to the image and the overall presentation, in that it should present clearly on monitors set to either DPI setting. In most cases when viewed on a 72 DPI monitor, the image will be slightly larger (in file-size) and have some extra information, but it’s a worthy trade-off for the extensibility it gives our presentation.

Save for the Web

In this step it is important that we find the best trade-off between file size and quality. If the image editing program you are using has a Save for Web feature, select it, otherwise save the image as a JPG or GIF. Generally, JPG compression (at a setting of ‘High’ or ‘Maximum’) gives good results for photos and color-intensive images, while GIF is good for line drawings and simple images. Play with the settings and try to get the file-size as small as possible without noticeably compromising the image quality.

Final Notes

Let’s hope following the recommendations and steps above has resulted in a satisfactory result. Test your presentation on the target computer, and remember to verify that its screen resolution matches what you’ve defined for your presentation.

If the result is still not to your satisfaction, reopen the uncompressed version of the image you saved for your records and experiment with modified settings. First, try saving the image in the format you did earlier, but use less compression. This is defined with the Quality selector for JPG, and with the Colors selector for GIF. If you’re still dissatisfied, try saving the image as a TIFF or PICT—this is an uncompressed file format that will not compromise the original image at all, but produces a large file-size and for that reason should be used as a last resort.

While an attempt has been made to cover the major considerations one encounters while acquiring an image and importing it into PowerPoint, this document is by no means comprehensive. Digital imaging is complex and multi-faceted, but hopefully this whitepaper has reinforced the fundamentals of image acquisition and improved the quality and appeal of your PowerPoint presentation.